5'37.  g 

M 2 REMOTE  STORAGE 

IS  ^'1 

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DCCLXVU 


NOTES  ON  RATING  ELECTRIC  POWER  PLANTS  UPON 
THE  HEAT-UNIT  STANDARD. 


(SECOND  PAPER.) 

BY  WM.  S.  ALDRICH,  MORGANTOWN,  W.  VA. 

(Member  of  the  Society.) 


These  notes  refer  to  a paper  t on  this  subject  read  by  the 
author  before  the  Hartford  meeting  (May,  1897)  of  this  Society. 
No  comparative  data  were  given  in  the  original  paper.  It  was 
known  that  the  Committee  on  Data  of  the  National  Electric 
Light  Association  had  a report  in  preparation  for  the  Niagara 
Falls  convention,  June  8,  1897.  This  was  the  fourth  and 
probably  the  last  of  such  valuable  reports.  It  was  deemed  ex- 
pedient, rather  than  refer  to  the  previous  reports,  to  await  the 
publication  of  the  1897  report  for  the  data  needed  in  discussion 
of  the  author’s  paper. 

The  earlier  reports  of  the  above  Committee  on  Data  have 
been  full  of  instructive  information  relating  to  many  types  of 
steam-power  electric  plants.  In  all  of  the  cases  finally  reported, 
their  rating  has  been  based  on  watt-hours  per  pound  of  coal. 
Over  three  years  ago  Mr.  F.  M.  Eites,  at  the  Montreal  meeting 
of  our  Society,  discussed  the  data  of  the  Washington  conven- 
tion of  the  association  (1894).  His  remarks  X at  that  time  were 


b * To  be  presented  at  tbe  New  York  meeting  (December,  J897)  of  the  American 
| Society  of  Mechanical  Engineers,  and  forming  part  of  Volume  XIX.  of  the 
| Transactions. 

f Transactions  of  the  American  Society  of  Mechanical  Engineers,  vol.  xviii., 
| No.  738,  “On  Rating  Electric  Power  Plants  upon  the  Heat-Unit  Standard,”  fry 
William  S.  Aldrich. 

X Transactions  of  the  American  Society  of  Mechanical  Engineers,  vol.  xv.,  No. 
I 509,  “ A New  Method  of  Compound  Steam  Distribution,”  by  F.  M.  Rites. 


2 RATING  ELECTRIC  POWER  PLANTS  I HEAT-UNIT  STANDARD. 

so  pertinent  to  tlie  whole  question  of  the  economy  of  electric 
power  plants  that  it  will  not  be  amiss  to  quote  them  here. 

“ It  is  impossible  that  competent  engineering  ability  should 
be  confined  exclusively  to  the  manufacturing  industries. 

“ It  cannot  be  assumed  that  the  average  intelligence  of  the 
designers  and  operators  of  electric  light  stations  is  inferior  to 
that  displayed  in  establishments  of  different  character,  and  yet 
the  enormous  discrepancy  between  the  actual  results  and  those 
which  should  be  realized  surely  deserves  some  attempt  at 
explanation. 

“It  is  but  proper  to  note  that  the  Committee  has  chosen  the 
record  of  a very  high  duty  as  a basis  of  comparison,  and  that  the 
nature  of  the  exacting  service  of  electric  light  and  street  railway 
plants  precludes  the  possibility  of  a close  approximation  to  the 
highest  economy  under  more  favorable  conditions ; but  these 
figures  are  entirely  unexpected  and  incidentally  somewhat  ridic- 
ulous, considering  the  energy  with  which  the  last  per  cent,  of 
efficiency  of  the  electric  apparatus  is  insisted  on  by  its  users. 

“ Possibly  some  reason  for  such  a remarkable  state  of  things 
may  be  found  in  the  miscellaneous  engineering  errors  which 
usually  follow  an  ignorantly  wasteful  policy,  but  these  are  as 
frequently  met  in  other  power  plants.  Perhaps,  also,  stations 
improperly  proportioned  and  generally  unfitted  for  economic 
competition  may  be  found  in  the  list,  but  these  are  far  from 
sufficient  to  account  for  such  universal  failure  to  realize  even  a 
moderate  degree  of  efficiency. 

“ There  seems'to  be  but  one  general  explanation  applicable  to 
electric  light  or  railway  stations  which  can  account  with  any 
degree  of  probability  for  such  extravagant  fuel  consumption, 
and  that  is  the  excessive  wastefulness  of  the  steam-engine  under 
varying  conditions  of  load.” 

Tt  is  proposed  in  the  present  paper  (I.)  to  discuss  briefly  the 
progress  shown  during  the  past  four  years  in  the  economic  per- 
formance of  steam-power  electric  plants  as  summarized  by  the 
Committee  on  Data  of  the  National  Electric  Light  Association ; 
(II.)  to  show  that  the  very  low  economy  of  such  electric-light 
and  railway  stations  is  not  entirely  due  to  uneconomical  engines 
and  variable  loads ; (III.)  to  present  a few  notes  upon  a further 
consideration  of  the  heat-unit  rating  for  such  plants.  This 
treatment  will  have  specially  in  view  the  necessity  for  some 
standard  rating  by  means  of  which  the  design,  installation,  test- 


RATING  ELECTRIC  POWER  PLANTS  I HEAT-UNIT  STANDARD.  3 

ing,  and  management,  as  well  as  specifications  and  contracts  for 
these  plants,  may  be  reduced  to  a satisfactory  basis  for  advanc- 
ing this  industry  along  engineering  lines. 

I. — PERFORMANCE  OF  ELECTRIC  POWER  PLANTS  ON  A COAL  BASIS. 

From  the  several  reports  of  the  Committee  on  Data  of  the 
National  Electric  Light  Association,  Tables  I.  and  II.  have  been 
compiled.  An  inspection  of  these  will  show  what  little  progress 
has  been  made  during  the  last  four  years  in  such  installations. 
In  fact,  the  expectations  of  the  (1894)  committee  seem  not  to 
have  been  realized  in  that  they  looked  for  much  better  values 
in  the  reports  of  subsequent  years.  It  is  a matter  with  which 
the  mechanical  engineer  is  most  directly  concerned.  His  work 
in  the  design  and  installation  of  even  the  most  recent  central 
station  is  open  to  criticism  that  cannot  be  applied  to  the  elec- 
trical features  of  the  same.  Electrical  engineers  themselves 
acknowledge  that  the  efficiency  of  the  modern  dynamo  has  prac- 
tically reached  the  limit  set  by  structural  and  economic  consid- 
erations. Mr.  Kites’  remarks,  quoted  above,  are  singularly  ap- 
plicable to  the  conditions  existing  at  the  present  day.  In  the 
light  of  what  he  has  said,  the  following  comparative  data  should 
be  carefully  studied  by  the  mechanical  engineer. 

TABLE  I. 

Showing  Results  of  Four  Years’  Progress  in  the  Economic  Per- 
formance of  Steam-power  Electric  Plants. 


Year. 

Convention  of  the  Nat. 
Electric  Light  Assoc., 
at— 

No.  of  Stations 

Watt-hours  per  Pound  of  Coau. 

Reported. 

Maximum. 

Minimum. 

Average. 

1894. . 

Washington 

65 

208 

25 

91.7 

1895.  .1 

Cleveland 

24 

262 

36 

128 

1896. . 

New  York 

81 

237 

33 

108 

1897.. 

Buffalo 

14 

269.5 

98.7 

156 

4 


EATING  ELEGTEIC  TOWEE  PLANTS  I HEAT-UNIT  STANDAED. 


TABLE  II. 

Equipment  of  the  Stations  Given  in  Table  I.,  Showing  the  Maximum 
and  Minimum  Economy. 


Year. 

Economy. 

Boilers. 

Engines. 

Dynamos. 

Daily  Out- 
put, Watt- 
hours. 

Fuel. 

r 

1894  \ 

l 

Maximum 

1 

Arc,  Power, and 
Incandescent. 
Arc  and  Incan- 

7,971,600 

80,670 

Coal,  Hard 

(208) 

Minimum 

! | 

Screenings. 

Coal. 

(25) 

! 

descent. 

f 

1895  \ 

l 

Maximum 

(262) 

Minimum 

(36) 

Horizontal  Water 
Tube. 

Horizontal  Tubu- 
lar. 

Trip.  Exp.  Con- D i rect  Con- 
densing. 1 nected. 

High  S p e e d Belted  Direct. 
Non-cond’g.  I 

22,967,952 

2,790,565 

i Soft  Coal,  i 
Hd.  Scn  en’gs. 
Bitumin.  Pea. 

r 

1896  -j 

l 

Maximum 
(23  7) 

Minimum 

(33) 

Horizontal  Tubu- 
lar. 

Horizontal  Tubu- 

High  Speed  Belted  Direct. 
Comp.  Cond’g 

High  S peed  Belted  Direct. 
Condensing.  1 

3,270,392 

203,555 

Bitumin.  Lump. 

Anthracite 

Buckwheat. 

f 

Maximum 

Water  Tube. 

Vertical  Couid.  Dir.  Connected. 

1837 1 

(2:19.5) 

Minimum 

Horiz.  Tubular. . . 

Cond’g  4-Valve 
Comp.  Cond’g. 
Comp.  Cond’g. 

Incandescent. 
Belted  to  Dyn., 
Belted  to  C.-Sh. 

Screenings. 

l 

(98. 7) 

and  Water  Tube. 

A comparison  of  tlie  above  with  some  of  the  best  results  ob- 
tained in  modern  mill  engines  has  been  noted  by  the  commit- 
tee, as  follows  : 

In  the  1894  report  compared  to  the  performance  of  the  engine 
of  the  Chelsea  Jute  Mills,  Brooklyn,  N.  Y.,  showing  a coal  con- 
sumption of  1.482  pounds  per  indicated  horse-power  per  hour? 
with  the  load  varying  from  495.21  to  764.96  horse-power.  If 
such  a performance  were  possible  in  the  central  station,  it  should 
result  in  over  409  watt-hours  per  pound  of  coal,  on  the  basis  of 
the  committee’s  assumption  of  90  per  cent,  for  the  mechanical 
efficiency  of  the  engine  and  for  the  same  efficiency  in  the  dynamo. 

In  the  1896  report  the  committee  called  attention  to  the 
then  world’s  record  for  steam  economy  as  shown  by  the  Chest- 
nut Hill  pumping  station  engine  at  Boston — a steam  con- 
sumption of  11.22  pounds  per  horse-power  per  hour,  or  an  effec- 
tive pump  liorse-power  per  hour  on  1.34  pounds  of  coal.  If  the 
efficiency  of  the  direct-connected  electric  generators  should 
compare  favorably  with  that  of  the  pumps  of  this  engine,  with 
no  allowance  for  variation  in  load,  anthracite  coal  used  in  the 
plant  with  the  same  economy  of  installation  should  produce  557 
watt-hours  per  pound  of  coal. 

In  the  1897  report  of  the  committee,  Mr.  F.  R.  Low,  member 
of  our  Society,  very  fully  discussed  the  several  sources  of  loss 


EATIN’G  ELECTRIC  POWER  PLANTS  : HEAT-UNIT  STANDARD.  5 


in  tlie  electric  power  plant,  stating  the  discrepancies  would  be 
made  up  mainly  from  the  following  items  : (1)  Decreased  boiler 
efficiency  ; (2)  lesser  normal  efficiency  of  engine  ; (3)  impaired 
conditions  of  engines ; (4)  unfavorable  engine  load ; (5)  leak- 
age ; (6)  condensation;  (7)  auxiliaries;  (8)  heating.  It  is  not 
our  purpose  to  discuss  this  admirable  report ; but  there  is  no 
reason  why  every  feature  of  installation  of  an  electric  power 
plant  should  not  be  as  fully  considered  in  design  and  construc- 
tion as  in  the  case  of  the  modern  high-duty  pumping  station. 
In  fact,  it  has  been  repeatedly  pointed  out  that  the  chief  dif- 
ferences are  those  due  to  the  running  conditions  of  electric 
plants,  and  not  entirely  due  to  sudden  and  wide  variations  of 
load.  Messrs.  A.  G.  Pierce  and  R S.  Hale  report  * of  the  per- 
formance of  the  Boston  stations  of  the  Edison  companies  : “ In 
our  test  we  have  finally  found  the  variation  due  to  causes  which 
we  first  thought  negligible,  to  be  more  than  the  variation  due 
to  the  change  of  load.” 

In  this  connection  it  is  important  to  notice  the  results  of 
Mr.  H.  A.  Foster’s  analysis  of  the  tests  of  twenty-two  different 
power  plants,  f These  included  manufacturing  establishments  3 
electric-light  stations,  pumping  engines,  etc.  Plants  above  200 
horse-power  show  a remarkable  uniformity  in  fixed  charges  ; 
namely,  interest  on  first  cost,  depreciation,  taxes,  and  insurance. 
The  operating  expenses  gradually  decrease  in  plants  from  200 
to  1,000  horse-power,  above  which  capacity  the  operating  ex- 
penses seem  to  remain  remarkably  uniform  and  quite  irrespec- 
tive of  load  variations.  The  large  electric  stations  supplying 
many  smaller  industries  are  scarcely  affected  by  the  instan- 
taneous load  changes  in  one  or  more  of  these  particulars. 

The  conclusions  to  be  drawn  from  all  of  the  preceding 
clearly  indie ate  that  the  economy  of  the  modern  high-duty 
pumping-engine  plant  is  due  to  a refinement  of  design  and 
economic  arrangement  of  the  installation  that  has  not  yet  been 
reached  in  the  electric  power  plant.  Anything  which  tends  to 
advance  the  latter  industry  along  the  lines  which  have  been  so 
clearly  marked  out  in  the  development  of  the  former,  merit  the 

* Quoted  by  Mr.  F.  R.  Low,  rcpo*t  of  Committee  on  Data,  National  Electric 
Light  Association,  Buffalo  meeting,  June  8,  1897. 

•f  Transactions  of  the  American  Institute  of  Electrical  Engineers,  vol.  xiv., 
“ V ariations  in  the  Cost  of  Steam  Power,”  by  Mr.  H.  A.  Foster.  Paper  pre- 
sented at  the  annual  convention,  July  28,  1897. 


6 


EATING  ELECTRIC  POWER  PLANTS  : HEAT-UNIT  STANDARD. 


attention  of  those  having  such  work  in  hand.  It  is  believed 
that  the  standard  heat-unit  specifications  aud  the  subsequent 
contract  trials  of  pumping  plants  upon  this  basis  have  combined 
to  develop  this  industry  to  an  unprecedented  degree. 

It  is  not  therefore  too  much  to  expect  that  similar  standard 
heat-unit  specifications  and  contract  trials  of  electric  power 
plants  will  advance  this  industry  also  along  the  same  engineer- 
ing lines.  At  least  the  efficiencies,  economies,  guarantees,  and 
contracts  now  being  realized  in  pumping  stations  should  be 
much  more  nearly  approached  by  the  modern  electric  power 
plant. 

II. — PLANT  ECONOMY  AS  RELATED  TO  ENGINE  ECONOMY  AND  VARI- 
ABLE LOADS. 

This  seems  to  be  the  chief  feature  of  Mr.  Rites’  explanation 
of  the  very  low  economy  of  the  electric  power  plants  reported 
upon  up  to  the  time  of  his  paper  previously  referred  to.  We 
certainly  do  not  wish  to  be  misunderstood  as  taking  issue  with 
this  explanation ; but  it  is  apparent,  from  a careful  study  of  the 
last  four  years’  record  of  the  Committee  on  Data,  that  some 
very  uneconomical  engines  have  produced  remarkable  results  in 
point  of  economy  of  operation  and  efficiency  of  installation. 
The  best  of  engines  may  be  poorly  operated  on  the  one  hand, 
and  the  whole  plant  badly  arranged  on  the  other  hand. 

We  enter  as  strong  a plea  as  any  one  for  the  most  economical 
engine  in  electric  power  plants  ; but  we  wish  to  add  a further 
requirement,  that  there  should  be  economic  installation  and 
efficient  operation  to  produce  the  best  all-round  results  in  the 
course  of  a day,  a month,  or  a year.  We  think  these  two  feat- 
ures may  possibly  have  produced  the  lowest  cost  of  steam 
power  yet  recorded  ; namely,  $11.55  per  year  of  3,070  working 
hours,  reported  by  Dr.  R.  H.  Thurston,*  member  of  our  Society. 
The  plant  is  at  the  Warren  Steam  Cotton  Mill,  Providence,  R.  I. 
The  1,950  horse-power  “ Allis  ” cross-compound  condensing 
engine  (cylinders  : 32  and  68  inches  by  5 feet  stroke,  74  revolu- 
tions per  minute),  with  Heine  water-tube  boilers,  at  155  pounds 
steam  pressure,  show  an  economic  performance  of  1.35  pounds 
coal  per  horse-power  per  hour. 

The  question  will  continue  to  be  asked  : Why  are  not  such 


Reported  by  Dr.  R.  H.  Thurston,  in  Science , October  1,  1897. 


FATING  ELECTRIC  POWER  PLANTS  : HEAT-UNIT  STANDARD.  7 


results  obtainable  in  electric  power  plants  with  similar  units  ? 
Low  cost  of  steam  power  or  of  electric  power  is  not  due  entirely 
to  multiple-expansion  engines  of  the  greatest  individual  econ- 
omy ; for  in  the  last  noted  instance,  as  reported  by  Dr.  Thurs- 
ton, the  cross-compound  condensing  engine  replaced  a quadru- 
ple-expansion engine. 

Concerning  the  effect  of  variation  of  load  upon  modern  elec- 
tric power  plant  engines,  it  is  further  interesting  to  note  that 
Messrs.  A.  G-.  Pierce  and  It.  S.  Hale  state  of  the  Boston  Edison 
stations  in  the  report  previously  noted : “As  a matter  of  fact, 
the  steam  per  indicated  liorse-power  in  our  two  200  units  holds 
within  12  per  cent,  over  a range  from  | up  to  full  out-put.” 

Along  the  same  line  it  is  to  be  noted  that  throughout  quite  a 
wide  range  of  load  variation  the  compound  engines  reported 
by  Mr.  A.  K.  Mansfield,*  at  the  recent  Hartford  meeting,  show 
a remarkably  uniform  rate  of  steam  consumption.  The  ques- 
tion naturally  arises  whether  such  uniformity  under  wide  varia- 
tions of  load  is  not  more  of  a characteristic  of  compound  engines 
than  formerly  considered  by  those  who  lay  all  the  blame  upon 
the  steam  engine  for  the  poor  showing  in  the  economy  of  elec- 
tric power  stations. 

With  dynamos  which  electrical  engineers  now  design  and 
build,  maintaining  an  efficiency  over  93  per  cent,  from  about  J 
load  to  20  per  cent,  over  load,  directly  coupled  to  cross-com- 
pound condensing  engines  (let  us  say)  which  mechanical  engi- 
neers are  designing  and  building,  having  a characteristic  low 
range  of  steam  consumption  between  similar  limits  of  light  load 
and  over  load,  the  question  will  naturally  arise  : Why  cannot 
the  two  units  be  more  economically  put  together,  installed,  and 
operated  ? 

III.— NOTES  ON  HEAT-UNIT  RATING. 

In  the  discussion  which  followed  the  presentation  of  the 
author’s  paper  on  this  subject  before  the  Hartford  meeting,  as 
well  as  in  conference  with  members  and  other  electrical  and 
mechanical  engineers  since,  it  will  appear  that  the  following 
points  have  been  brought  out : 

That  the  heat-unit,  as  a basis  for  such  ratings,  is  both  rational 

* Transactions  of  tlie  American  Society  of  Mechanical  Engineers,  vol.  xviii., 
No.  727,  “The  Best  Load  for  the  Compound  Steam  Engine/’ by  Mr.  A.  K. 
Mansfield. 


8 RATING  ELECTRIC  TOWER  PLANTS  : HEAT-UNIT  STANDARD. 

and  scientific.  It  is,  however,  not  in  consequence  the  most 
satisfactory  standard  for  use  by  builders,  contractors,  and  prac- 
tical engineers  dealing  with  this  class  of  motive-power  machin- 
ery ; namely,  steam  engines  and  dynamos. 

That  great  differences  of  opinion  exist  as  to  the  proper  defini- 
tion of  the  heat-unit  required  for  such  a standard.  There  are  at 
least  four  different  heat-units  commonly  employed. 

That  the  present  extensive  and  satisfactory  use  of  the  lieat- 
unit  for  steam-pumping  installations  is  as  it  should  be  and  is 
all  right  in  that  place ; but  this  is  no  argument  for  its  introduc- 
tion and  use  in  a similar  manner  in  the  rating  of  steam  electric 
plants. 

That  the  present  way  of  stating  the  performance  of  electric 
power  plants,  however  unsatisfactory,  is  easily  understood  by 
all  parties  interested.  Chief  of  these,  of  course,  is  the  capitalist ; 
he  can  readily  comprehend  rating  based  on  the  coal  bill. 

That  the  load  factor,  after  all,  has  not  so  much  to  do  with  the 
fuel  economy  of  the  plant,  as  such,  however  much  the  varying 
loads  may  individually  affect  any  of  the  units  of  the  installation, 
such  as  the  steam-engine.  Therefore,  in  the  large  city  and 
suburban  steam-power  and  electric  plants  now  being  installed, 
there  is  not  the  necessity  for  such  strict  adherence  to  eco- 
nomic load  factors  as  in  the  case  of  plants  with  smaller  units. 

That  the  watt  expresses  the  activity  or  rate  of  the  electrical 
output,  in  joules  per  second.  In  this  respect  it  is  analogous 
to  the  horse-power  rating  of  mechanical  output.  Hence,  the 
standard  rating  should  be  in  kilowatt-hours  per  1,000,000  B.T.U. 
supplied  to  the  steam  used  in  the  whole  plant. 

That  if  the  heat-unit  basis  is  considered  as  the  proper  stand- 
ard for  the  steam  electric  plant,  the  whole  heat  supplied  to  the 
plant  should  be  as  carefully  determined,  and  in  the  same  man- 
ner, as  now  in  vogue  for  similar  standard  ratings  and  contract 
trials  for  steam -pumping  plants. 

That  the  boiler  should  be  in  evidence  in  all  cases  in  which 
plant  performance  is  mentioned.  In  the  electric  plant  it  is 
economy  of  installation  that  is  desired  quite  as  much  as  in 
the  case  of  pumping  plants.  Why  should  the  boiler  perfor- 
mance be  urged  into  consideration  in  the  former  case  and  not 
in  the  latter  ? If  it  is  a good  thing  to  introduce  it  in  either  case 
it  would  seem  proper  to  do  so  in  both  cases. 

That  the  common  rating  of  performance  of  pumping  plants  in 


RATING  ELECTRIC  POWER  PLANTS  : HEAT-GNIT  STANDARD. 


9 


foot-pounds  per  1,000  pounds  steam  would  be  amply  sufficient 
for  all  purposes  of  rating  electric  plants  for  which  the  heat-unit 
basis  is  advocated.  This  seems  particularly  plausible  on  ac- 
count of  the  small  variation  in  the  total  heat  of  one  pound  of 
steam  for  quite  a wide  range  of  pressures  now  used  in  modern 
electric  plants.  Taking  the  standard  temperature  of  feed  water 
at  212  degrees  Fahr.  exactly  1,000  B.T.U.  are  required  to  raise 
the  temperature  and  evaporate  one  pound  of  feed  water  into 
steam  at  77.3  pounds  per  gauge  (92  pounds  abs.).  Taking  this 
as  suitable  for  a simple  non-condensing  engine,  we  may  compare 
it  with  that  of  150.3  pounds  gauge  (165  pounds  abs.),  in  which 
1 013.5  B.T.U.  are  required  to  raise  the  temperature  from 
feed  water  (212  degrees  Fahr.)  and  evaporate  it  into  steam  at 
the  given  pressure..  In  this  case,  therefore,  if  we  adopt  1,000 
pounds  steam  instead  of  the  1,000,000  B.T.U.,  we  make  an  error 
of  only  1.3  per  cent.  It  is  claimed  that  this  is  within  the  usual 
allowable  errors  of  observation  and  measurements  in  power- 
plant  tests,  and  that  there  is  not  enough  difference  to  warrant 
the  trouble  required  to  obtain  the  performance  reduced  to  a 
B.T.U.  standard. 

In  this  connection  it  is  interesting  to  note  the  progress  shown 
by  the  committee  reports  on  data  made  to  the  National  Electric 
Light  Association.  In  eleven  out  of  the  fourteen  cases  noted 
in  the  report  presented  at  the  Buffalo  meeting  of  that  associa- 
tion, the  water  per  kilowatt-hour  at  best  efficiency  of  the  en- 
gine is  noted.  As  t the  average  temperature  of  the  feed  water  in 
the  best  stations  reported  is  from  208  to  212  degrees  Fahr.,  and 
the  best  results  are  shown  by  the  compound  condensing  en- 
gines, we  may  conclude  that  the  comparative  water  ratings  are 
within  about  1 per  cent,  of  what  such  comparative  ratings  would 
be  if  based  on  the  B.T.U.  standard. 

It  is  a question  whether  mechanical  engineers  will  remain 
satisfied  with  results  even  within  this  close  degree  of  approx- 
imation. The  fact  has  been  repeatedly  pointed  out  by  elec- 
trical engineers  that  their  system  of  units  is  altogether  unique, 
is  thoroughly  scientific  (being  based  upon  the  C.  G.  S.  system 
and  is  the  only  system  of  engineering  units  universally  adopted. 
Mistakes  are  said  to  be  occasionally  avoided  in  the  sister  pro- 
fession of  mechanical  engineering  by  the  insistence  on  the  ac- 
curate use  of  terms  and  of  units  in  electrical  engineering. 
Dealers  in  electrical  stocks  and  capitalists  exploiting  electrical 


10  EATING  ELECTRIC  POWER  PLANTS  : HEAT-UNIT  STANDARD. 

enterprises  generally  have  an  appreciative  insight  into  the 
meaning  of  volts,  amperes,  and  kilowatts.  Why  should  the 
time-honored  heat-unit  be  so  difficult  of  comprehension  by  the 
same  class  of  interested  citizens  ? 

A quarter  of  a century  ago  Maxwell  wrote  : “ The  conse- 
quences of  this  demand  for  electrical  knowledge  and  of  these 
experimental  opportunities  for  acquiring  it  have  been  already 
very  great  both  in  stimulating  the  energies  of  the  advanced 
electrician  and  in  diffusing  among  practical  men  a degree  of 
accurate  knowledge  which  is  likely  to  conduce  to  the  general 
scientific  progress  of  the  whole  engineering  profession.” 


